Moaddel, R., Venkata, S. L. V., Tanga, M. J., Bupp, J. E., Green, C. E., Iyer, L., … & Wainer, I. W. (2010). A parallel chiral–achiral liquid chromatographic method for the determination of the stereoisomers of ketamine and ketamine metabolites in the plasma and urine of patients with complex regional pain syndrome. Talanta, 82(5), 1892-1904.
A parallel chiral/achiral LC–MS/MS assay has been developed and validated to measure the plasma and urine concentrations of the enantiomers of ketamine, (R)- and (S)-Ket, in complex regional pain syndrome (CRPS) patients receiving a 5-day continuous infusion of a sub-anesthetic dose of (R,S)-Ket. The method was also validated for the determination of the enantiomers of the Ket metabolites norketamine, (R)- and (S)-norKet and dehydronorketamine, (R)- and (S)-DHNK, as well as the diastereomeric metabolites hydroxynorketamine, (2S,6S)-/(2R,6R)-HNK and two hydroxyketamines, (2S,6S)-HKet and (2S,6R)-Hket. In this method, (R,S)-Ket, (R,S)-norKet and (R,S)-DHNK and the diastereomeric hydroxyl-metabolites were separated and quantified using a C18 stationary phase and the relative enantiomeric concentrations of (R,S)-Ket, (R,S)-norKet and (R,S)-DHNK were determined using an AGP-CSP. The analysis of the results of microsomal incubations of (R)- and (S)-Ket and a plasma and urine sample from a CRPS patient indicated the presence of 10 additional compounds and glucuronides. The data from the analysis of the patient sample also demonstrated that a series of HNK metabolites were the primary metabolites in plasma and (R)- and (S)-DHNK were the major metabolites found in urine. The results suggest that norKet is the initial, but not the primary metabolite and that downstream norKet metabolites play a role in (R,S)-Ket-related pain relief in CRPS patients.